Unintuitive "no default font" for instance extraction with no instance defined on origin master

From a user’s perspective: When extracting UFO instances from a Glyphs file it seems unintuitive to require a default font on the master locations that are not used as instances.

Imagine two axes with ranges 0-100 and four masters at 0,0 - 0,100 - 100,0 - 100,100. If the instances are located e.g. on 25,25 - 25,75 - 75,25 - 75,75 the extraction will fail with error `fontmake.instantiator.InstantiatorError: Can't generate UFOs from this designspace: no default font.` Fontmake requires an instance at 0,0 (or whatever is set as the Variable Font Origin in GlyphsApp, I presume), even though as instance it is superfluous to the instances I am actually generating. Manually inserting a dummy instance at the specified master gets you around this, but if this is purely a designspace validation issue, could that not happen behind the scenes?

Note that prior to 2.x this setup was no issue and instances could be extracted without the need for a coninciding Origin master.